It is known to treat fluids, such as air and water, by ultraviolet (UV) light for disinfection. In order to obtain reliable results, corresponding treatment devices need to ascertain that the fluid to be treated has been irradiated by a sufficient quantity of UV light to ensure a desired level of disinfection.
Measuring a dosage value involves to measure not only an irradiance level, but to also integrate the measured irradiance level over time, and, possibly, over different wavelengths and spatial directions. In the case of a moving irradiated object, such as a fluid stream, dosage measurement additionally has to consider movement of the fluid, e.g. by measuring a flow speed.
US-A-2004/0061069 relates to a fluid treatment system with an UV sensor and an intelligent driver. Within the system, a fluid is irradiated with ultraviolet light. A sensor detects an UV intensity level and a flow of the fluid stream. The intensity is detected by a photodiode. Flow of the fluid stream is detected by a vibration-sensitive microphone. The system further includes an intelligent driver that powers a UV lamp in dependence on measured parameters.